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Chemistry: Post your doubts here!

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sagar65265

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GCE As and a level said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w07_qp_1.pdf
Q9 , Q26 . Q37
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_11.pdf
Q21 , 23 , 32
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_12.pdf
Q20 , Q25
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s07_qp_1.pdf
Q25,26,38
PLZ GUYS
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Q20)

When esters are hydrolysed using alkalis under reflux, not only is the reaction a one-way reaction (no equilibrium mixture is formed, reaction is complete) but in the end, the ester is split into an alcohol and acid, the ones that formed it in the first place. However, there is a twist here - the acid reacts with any excess alkali and forms the metal salt of that alkali.

So, in this case we use sodium hydroxide, NaOH, to hydrolyse propyl ethanoate. The products of that hydrolysis are normally Ethanoic Acid, CH3COOH and Propanol, CH3CH2CH2OH. So, the acid forms the Sodium Salt, which means that we get Sodium Ethanoate instead of Ethanoic acid, so we get CH3COONa.

The mass per mole of Propanol is (Mass of all Carbon atoms in molecule + Mass of all Hydrogen atoms in molecule + Mass of all oxygen atoms in molecule) =
(3 * 12 + 8 * 1 + 1 * 16) = 60 grams per mole.

The mass per mole of Ethanoic Acid is (Mass of all Carbon atoms in molecule + Mass of all Hydrogen atoms in Molecule + Mass of all Oxygen atoms in molecule + Mass of all Sodium atoms in Molecule) = (2 * 12 + 3 * 1 + 2 * 16 + 1 * 23) = 82.

Adding this up, the total mass of the organic products (no other carbon-containing products are formed) is equal to 60 + 82 = 142 grams.

The percentage of CH3CH2CH2OH = 60/142 * 100 = 42.25 % = 42.3 %.
The other one must automatically be 100 - 42.3 = 57.7 %.
This means our answer should be C.

I'm running late right now, hope this helped.

Good Luck for all your exams!
 
GCE As and a level

GCE As and a level

Messages
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sagar65265 said:
Q20)

When esters are hydrolysed using alkalis under reflux, not only is the reaction a one-way reaction (no equilibrium mixture is formed, reaction is complete) but in the end, the ester is split into an alcohol and acid, the ones that formed it in the first place. However, there is a twist here - the acid reacts with any excess alkali and forms the metal salt of that alkali.

So, in this case we use sodium hydroxide, NaOH, to hydrolyse propyl ethanoate. The products of that hydrolysis are normally Ethanoic Acid, CH3COOH and Propanol, CH3CH2CH2OH. So, the acid forms the Sodium Salt, which means that we get Sodium Ethanoate instead of Ethanoic acid, so we get CH3COONa.

The mass per mole of Propanol is (Mass of all Carbon atoms in molecule + Mass of all Hydrogen atoms in molecule + Mass of all oxygen atoms in molecule) =
(3 * 12 + 8 * 1 + 1 * 16) = 60 grams per mole.

The mass per mole of Ethanoic Acid is (Mass of all Carbon atoms in molecule + Mass of all Hydrogen atoms in Molecule + Mass of all Oxygen atoms in molecule + Mass of all Sodium atoms in Molecule) = (2 * 12 + 3 * 1 + 2 * 16 + 1 * 23) = 82.

Adding this up, the total mass of the organic products (no other carbon-containing products are formed) is equal to 60 + 82 = 142 grams.

The percentage of CH3CH2CH2OH = 60/142 * 100 = 42.25 % = 42.3 %.
The other one must automatically be 100 - 42.3 = 57.7 %.
This means our answer should be C.

I'm running late right now, hope this helped.

Good Luck for all your exams!
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Thnx alot
remember me in ur prayers :)
 
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